Your eyesight might be better than mine. I can tell when I drop below 40-45 FPS, but I can't see the difference between 60 and 200. You might be able to. It would be worth checking out in a local shop before you spent that much on a monitor though.

Perhaps you can't notice the difference between 60 and 200 because likely your monitor is only 60Hz.

I have this monitor, got it yesterday from NCIX and it's truly fantastic. For optimal results however, your FPS will need to be above 100 (or around 100 at least).

If you can maintain a good FPS, 120Hz just makes games feel smooth as butter.